Somehow the "buy" button for Star Explorers has been disabled. I have contacted Steam Support, no word from them yet. Hopefully this will be resolved soon, sorry for any inconvenience.
As a result, I have also disabled the Schmidt Workshops Super-Fantastic MegaBundle, since Star Explorers is not included in it right now. It will be reactivated as soon as the game is available.
I wrote an article about this issue here:

